1. Field of the Invention
The invention concerns a sampling valve for liquid and gas streams, especially for coal gasification plants with a fixed bed and with a high solids content in the crude gas, reactors with gas streams having a high temperature level and the danger of condensation.
2. Discussion of the Prior Art
In particular, the Lurgi gasification process belongs to the coal gasification plants in question. In the process developed by Lurgi, the lumpy coal is preferably gasified at a pressure of 30 bars, but it can also be gasified at a pressure of up to 100 bars and above. In the process, the coal is gasified with steam and oxygen in a quaisi static heap (or bed) on a hearth. The coal is introduced into the gas generator via a lock (or charging valve) and a distributor. The gasifying agent flows in under the hearth, as a result of which a good distribution and uniform gasification is obtained. The coal passes through various zones which merge one into the other. The coal is dried, low-temperature carbonized, gasified in turn by the rising gases and finally burned. The resulting ash is removed, almost carbon-free, via a lock. The generators are surrounded by a water jacket. The steam produced therein is fed to the gasifying agent. The gas produced leaves the upper part of the generator. The easily cracked tar products are carried out with the crude gas together with the undecomposed steam and dust.
In the succeeding condensation and condensate-separation installations, a thick dust-containing tar is deposited which, as a rule, is fed back via a circuit into the generator. The dust is gasified and the finally obtained almost dust-free tar can be further processed with the other condensation products.
The optimization of the above-described procedures requires the considerable use of automatic control technology. As a result, the control of gasification reactors involves serious problems. The composition of the crude gas has, in this case, shown itself to be a control quantity which cannot be ignored. Hitherto, in order to obtain a sample, the desired amount of sample was drawn off at the earliest possible time, subsequent to the saturation and purification of the crude gas, from the gas exiting from the coal gasification reactor, using for this purpose a suitable connecting pipe. The connecting pipe discharges via an intermediate sampling valve into the gas pipe connected to the outlet side of the reactor or to the radiation and/or convection cooler connected to the outlet side of the reactor. Due to the pressure reigning in the gasification plant, crude gas flows into the connecting pipe on opening the sampling valve. The amount of sample obtained depends on the amount of time which elapses between opening and closing the sampling valve which closes the connecting pipe at its mouth.
However, the gas drawn-off as the sample is frequently not representative of the crude gas, the sampling being rendered difficult on account of the high temperature of the crude gas, its high pressure and the amount of solids in the gas which tend to precipitate when the temperature is reduced. In particular, the condensing-out of heavy hydrocarbons and chlorides impairs the trouble-proof operation of the sampling valves. This leads to an additional arrangement of sampling valves on the downstream side with their associated connecting pipes. In practice, these connecting places for the taking of samples are associated with the gas purifying stages. Apart from the drawback of having a serious delay in the measurement of the composition of the crude gas, there is associated with these locations the additional danger of condensation and hence concomitant blockages or falsifications of the drawn gas samples.
It is therefore an object of the invention to provide a sampling valve which can function reliably when located as closely as possible to the reactor.